1. The Field of the Invention
The present invention relates to semiconductor devices and the manufacture thereof. More particularly, the present invention is directed to a method for forming self-aligned integrated circuit structures employing a protective layer having a horizontal top surface.
2. The Relevant Technology
Self-aligned structures in an integrated circuit may be formed by shielding previously formed structures with a protective layer of a material that resists the etchant which is used to form spaces for the self-aligned structures. The protective layer shields underlying previously formed structures from the etchant, effectively preventing the etchant from etching away around the structures to be protected. Thus the alignment of the mask to the previously formed structures is much less critical, hence the name xe2x80x9cself-alignedxe2x80x9d. Such self-aligned structures allow denser spacing of circuit devices.
For successful formation of self-aligned structures such as self-aligned contact structures, the protective layer must adequately withstand the etchant which forms the spaces in which the self-aligned structures are to be formed. If a protective layer is etched through in the case of self-aligned contacts for example, the contact structures formed subsequently will contact inappropriate areas, resulting in shorted, non-functional circuit devices.
Protective layers over underlying structures are most vulnerable at top edges of the protective layer. Reducing the protective layer""s tendency to be etched through at such top edges would thus provide an important advantage, allowing the production of dense self-aligned circuit designs with increased process control and higher yield.
An object of the present invention is to provide an improved method for forming self-aligned integrated circuit structures, said method providing decreased likelihood of etch-through of a protective layer overlying the circuit structures.
Another object of the present invention is to provide an improved method for forming self-aligned integrated circuit structures, said method allowing the production of dense self-aligned circuit designs with increased process control and higher yield.
Another object of the present invention is to provide processes for forming on a substrate a raised structure including an outermost protective layer, said structure having a horizontal upper surface extending between substantially vertical lateral surfaces, said horizontal upward surface being horizontal over the entire area therebetween.
In accordance with the method of the present invention, raised structures each have thereon a vertical protective layer on lateral sides of the raised structure. The surface of the protective layer forms a vertical lateral surface over the raised structure. Each raised structure is provided with a horizontal upper surface extending between the vertical lateral surface. The horizontal upper surface is substantially horizontal over the entire area between the vertical lateral surface which circumscribes the horizontal upper surface. An etchable layer is provided over and between two or more of the raised structures, and a patterned photoresist layer is provided on the etchable layer.
The etchable layer is then etched anisotropically and selectively to the protective layer to form spaces between the raised structures. A fill layer is then deposited to fill the spaces between the raised structures. The material of the fill layer in the spaces is self-aligned to the raised structures. During the anisotropic etch of the etchable layer, the horizontal upper surface of the protective layer of each raised structure provides significantly improved resistance to, or selectivity of, etching at the top edges of the raised structure where the horizontal upper surface meets the vertical lateral surface. By forming a horizontal upper surface of the protective layer, there is an increase in process reliability, control, and yield.
Various planarization processes may be employed to form the horizontal upper surface of the protective layer of the raised structures, including chemical mechanical polishing and simultaneous etching.
These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.